Extrahepatic biliary atresia is a liver disease presenting in early infancy, manifested by progressive obliteration of the extrahepatic bile ducts. It has been estimated to occur in from one per 8000 to one per 15000 live births, and is the single most common indication for performance of liver transplantation in children. None of the incidence figures is based on a well defined geopolitical region; most estimates of the frequency of this condition are derived from referral centers. Some investigators have suggested a time-space clustering of this condition. This project has gathered birth certificates and other information on all cases occurring among children born over a period of 12 years in Ohio. Ninety-four (94) cases were identified, corresponding to a rate of 0.5 cases/10,000 births. Cases will be compared to the other births in the state for evidence of changes in incidence and clustering. A number of potential risk factors for the condition will be examined.